The invention concerns a process for surface-modification by physico-chemical reactions with the steps:
(a) contacting a solid surface having a crystalline or amorphous structure with a reactive, gaseous fluid (gas, gas mixture, vapor or vapor mixture) which is to interact with the surface, PA1 (b) supplying activating energy to the contact area between fluid and surface by means of ions or plasmas, in order to trigger reactions between said partners, PA1 (a) deposit coatings on the surface by the interaction of the gases, gas mixtures or vapors at a surface with ion beams or a plasma, which are composed of radicals of said gases or vapors, or PA1 (b) erode (etch) surface atoms by the interaction of the reactive fluids at the surface with ion beams or with a plasma by forming volatile molecules from surface atoms and radicals of the said gases or vapors, or PA1 (c) desorb, and so erode or etch, respectively, surface atoms or -molecules by the interaction of the ions at the surface. PA1 I. R. A. Haefer, "Oberflachen- und Dunnschicht-Technologie" ("Surface and Thin Film Technology") Part 2; "Oberflachenomodifikation durch Teilchen und Quanten" ("Surface Modification by Particles and Quanta") Series Werkstoff-Forschung und Technik (Materials Research and Technology), Volume 6, Springer 1991; PA1 II: "Low Energy Ion Beam and Plasma Modification of Materials", eds. J. M. E. Harper, K. Miyake, J. R. McNeil, and S. M. Gorbatkin, Symposium Proceedings of the Materials Research Society, Vol. 223, Materials Research Society, Pittsburgh, USA, 1991; PA1 III: Comptes Rendus des Travaux du "8eme Colloque International sur les Procedes Plasma" (Contributions to the "8th International Colloquium on Plasma Processes"), Le Vide les Couches Minces, Supplement 256, 1991,
as well as a device for the implementation of the process.
The process therefore includes for instance the coating or etching of surfaces by physicochemical reactions of reactive, gaseous fluids (gases, gas mixtures, vapors or vapor mixtures) at the surfaces, supported by plasmas or ion beams, which
It is known, that processes employing ion beams and plasmas in the presence of gases or vapors, depending on the choice of these gases or vapors, are used for the etching of surfaces, or the coating of surfaces, or for the production of thin films on surfaces. A summary of the foundations and of the technical state of the art of these processes is found in three publications:
referred to as I, II, and III, respectively.
Subsumed to the term "Surface-Modification" have to be particularly surface-coating and surface-etching.
For the coating of surfaces from gases or vapors, energy has to be locally supplied at the surface for the physico-chemical reaction of the gases or vapors to create bonding with the surface, in order to obtain the coating of the surface with the desired compound. That is why thermal energy supply allows for instance to produce Si.sub.3 N.sub.4 -coatings on SiO.sub.2 -films by streaming gases of SiH.sub.4 and N.sub.2 against surfaces of SiO.sub.2 -films heated to high temperatures (&gt;600.degree. C.). Such processes are called "Chemical Vapor Deposition", CVD. For many applications the CVD-process faces, however, the disadvantage to work only at high temperatures.
It is known, published application of the German Patent Office DE 4020816 A1, referred to as D1 in the following, to improve the CVD-process by special devices for the transport of reactants towards the surface, in order to obtain coatings with higher purity. To that end, in D1 for instance, substances are activated (ionized) by various methods and accelerated, then electromagnetically separated, and then decelerated and neutralized before they react at the surface to form a coating.
It is known, to work at reduced surface temperatures by supplying the energy for the physico-chemical reaction at the surface by impinging singly charged ions with kinetic energy. The ions may stem from a plasma or from an especially prepared ion beam.
In the case of a convectional plasma, one speaks of "Plasma Enhanced (or Activated) Chemical Vapor Deposition", PECVD or PACVD. With it one obtains a reduction of the surface temperature for the Si.sub.3 N.sub.4 -coating, described above, to about 300.degree. C. With the more recent "Electron Cyclotron Resonance", ECR-plasmas, this temperature can be further reduced to about 150.degree. C. One speaks then of ECR-PECVD, which is applied already, but is still subject of research for all its possible applications. On the progress with ECR-PECVD on the production of diamond coatings from the gas mixture of CH.sub.4 and H.sub.2 has been reported [F. Roy, M. Mermoux, B Marcus, III, pages 353 to 355].
The replacement of the plasma by an ion beam with single charge and energy allows a still better localization and concentration of the energy supplied for the CVD at or on the surface of the substrate and so allows a further reduction of the temperature of the substrate. This energy is mainly supplied by the absorption of the kinetic energy of the ions in the first surface layers in the form of a surface activation. One speaks therefore of "Ion Activated CVD", IACVD. This IACVD is of particular interest, since gases or gas mixtures which adsorb at the surface are activated together with the surface only by the ion bombardment and the resulting solid compounds are deposited as films. This technology yields good coating results especially at low temperatures (i.e. -100.degree. C.) of the substrates [M. Hirose, H. Shin, S. Miyazaki, and Y. Hriike, III, pages 105 to 112]. The type of ion is at free choice, so that ions of the coating to be deposited can be used, which yields coatings with higher purity. By using low energy C.sup.+ -ions for instance, diamond crystal coatings with high purity could be produced [J. W. Rabalais and S. Kasi, Science 239, (1988), page 623]. The tribologically important transition metal-nitride or -carbide coatings can also be well produced by using N.sup.+ - or C.sup.+ -ions.
For the surface etching with gaseous reactive fluids (gases or vapors), energy has to be locally supplied at the surface for the physico-chemical reaction of the gases or vapors with the surface. This energy mainly serves to liberate reactive radicals from the gas molecules which form together with the surface atoms volatile molecules and do so erode the surface. On hot Silicon surfaces, for instance, very reactive, neutral fluorine atoms are separated from CF.sub.4 (tetrafluoromethane) which form volatile SiF.sub.4 at the Si-surface and do so erode the Si-surface on a large scale.
When the dissociation is energetically supported by a plasma, for instance, reactive ions are also formed which serve for an increased etching of the surface. In the preceding example, CF.sub.3 .sup.+ -ions add to the etching besides the neutral fluorine atoms. In this case one speaks of "Reactive Ion Etching", RIE. The ions may have kinetic energies up to some 100 eV and do so not only dissociate the gas molecules, but cause also a physicochemical activation of the surface atoms. Since this activation depends on the direction of impact of the ions, spatially directed etching can be achieved in particular when the ion production is spatially separated from the region of the substrate. A directed ion beam can then interact with the substrate; the etching gas streams simultaneously towards the substrate. One then speaks of "Reactive Ion Beam Etching", RIBE. As examples may serve the etching of Al.sub.2 O.sub.3 or Au by Cl.sup.+ ions supported by simultaneous streams of CCl.sub.4 or C.sub.2 F.sub.4 Cl.sub.2 [I, chapter 7.6, pages 205 to 217].
It is an advantage of the RIBE-process that the gases or gas mixtures which adsorb on the surface are activated together with the surface only by the ion bombardment, combine with molecules (atoms) from the substrate and do so allow a well controlled etching of the surface. This technology yields precise etching results especially at low temperatures (e.g. -100.degree. C.), where the gases or gas mixtures are well adsorbed [M. Hirose. H. Shin, S. Miyazaki, and Y. Horiike, III, pages 105 to 112; R. Petri, J. -M. Francou, D. Henry, and A. Inard, III, pages 94 to 97].
In these ion assisted coating- or etching processes ion bombardment is disadvantageous that the kinetic energy of the ions, which is necessary for the creation of the local surface activation or for the local physico-chemical activation, is so high that a damage of the material beneath the surface and of the coating already deposited can not be avoided. These material defects have important consequences. Experiments have shown that electronic or opto-electronic components produced with these processes had too high a density of defects and could therefore not be used. Long lasting annealing processes had to be applied therefore, which ruined the technological advantages of the production process [D. Lootens, P. Clauws, P. Van Daele, and P. Demeester, III, pages 292 to 294].